Mesoscale Precipitation Discussion 0198
NWS Weather Prediction Center College Park MD
1045 PM EDT Sun Apr 28 2024

Areas affected...Southeast TX through Northwest LA

Concerning...Heavy rainfall...Flash flooding likely

Valid 290245Z - 290845Z

SUMMARY...Backbuilding and training showers and thunderstorms
across southeast TX and northwest LA are expected to continue to
produce areas of extreme rainfall over the next several hours.
Flash flooding will continue locally, and parts of southeast TX in
particular are expected to see significant and locally
life-threatening impacts.

DISCUSSION...GOES-E IR satellite imagery shows a very strong
cold-topped convective wedge signature over southeast TX with
persistent areas of backbuilding and training showers and
thunderstorms. Overshooting top activity with cloud top
temperatures occasionally as cold as -70C have been noted in a
southwest to northeast fashion from Brazos County to Trinity
County. Additional areas of strong, and slow-moving convection are
situated also farther northeast into northwest LA.

The convection is situated along a well-defined outflow boundary
with moderate to strong instability pooled along it which is being
aided by convergent and moist low to mid-level southwest flow.
MLCAPE values are on the order of 1500 to 2500 J/kg with PWs of
around 1.75 inches, and this is helping to yield extremely heavy
rainfall rates of as much as 2 to 4 inches/hour.

Enhanced upper-level divergence over the region is noted in the
IR/WV satellite imagery loops, and the southwest flank of the
ongoing axis of convection is expected to be an area over the next
few hours where convection is likely to continue to regenerate and
train over the same area.

Already there have been rainfall totals locally of 4 to 8 inches
in areas of southeast TX, and with the expectation of additional
extreme rainfall over the next several hours, some areas
especially in between northeast Brazos, northern Grimes, northern
Walker and Trinity Counties may see rainfall totals reach 8 to 12+
inches.

Recent runs of the HRRR guidance have been insisting on this
extreme rainfall potential, and as a result, significant and
locally life-threatening flash flooding is expected going through
a portion of the overnight period. WPC has upgraded a portion of
the MPD area to a Moderate Risk of excessive rainfall the D1 ERO
given the ongoing satellite and radar trends.

Orrison

ATTN...WFO...EWX...FWD...HGX...LCH...SHV...

ATTN...RFC...LMRFC...WGRFC...NWC...

LAT...LON   32899280 32619241 31929238 31109324 30529433
            30069594 30319671 30689666 31449616 32139531
            32729404 32869352